1. Field of the Invention
The present invention generally relates to boiler systems, and more particularly to a water-cooled oscillating grate system for a boiler for use with solid fuels.
2. Description of Related Art
Large-scale boilers are used in industrial processes and in power generation, among other applications. Fuel is fed into such boilers, and handled by an automatic or remotely operated grating system. Such gratings are typically movable or vibrating to facilitate combustion by mixing solid fuel held thereon. The gratings for stokers used in large-scale boiler systems are formed of multiple sections approximately 2 meters in width. Typically, steep walled hoppers are required underneath the gratings to collect ash siftings that fall through openings between grate sections. Also, multiple water pipes typically project from each end of the grate to stationary water headers. This arrangement adds cost, results in excess transmission of vibrations, and results in failure due to fatigue in the water pipes. In many vibrating grate systems excessive vibration is coupled to the boiler and the surrounding structure. This occurs, particularly when the grate is not effectively counter-balanced or isolated from the boiler.
U.S. Pat. No. 6,220,190 to Dumbaugh et al (“Dumbaugh”). addresses many of the foregoing problems with typical systems. In Dumbaugh, as illustrated in FIG. 8, a water-cooled grate unit 104 engages a boiler shell 118, at which interface an appropriate flexible connection is provided. Perimeter sealing connections between the boiler 102 and grate unit 104 are provided by a labyrinth type seal 170 and a flexible fabric expansion joint connection 174. The perimeter bladed labyrinth type seal connection 170 is provided in-line with the vibratory stroke angle of the vibration drive isolation assembly 112. The perimeter flexible fabric expansion joint 174 provides sealing for the boiler 102 thermal expansion movement. All four walls of air plenum chamber 108 are directly attached to the grate surface 106 with all four walls to provide a tight air seal.
In accordance with Dumbaugh, however, a protruding element, sometimes referred to as a “chill bar” is included on the boiler feed water supply line 119 for pushing fuel toward the middle of the grate. The fuel would otherwise approach a gap between the grating and the boiler. Although this arrangement may be suitable, such an arrangement may not lend itself easily to retrofit of an existing boiler. Additionally, lateral fuel migration is inhibited best when the boiler expands to the position indicated in FIG. 8 by dotted lines. Until the boiler reaches operating temperature, therefore, fuel and combustion gases may more easily escape. Further, the protrusion provided on the boiler feed water supply line 119 is not easily replaceable. Accordingly, if it is abraded by moving fuel, major repairs may be necessary, resulting in unnecessary boiler down time.
A need therefore exists to provide an improved water-cooled vibrating grate system that minimizes the vibration coupled to the boiler and the surrounding structure, which also addresses the need for a practical, reliable and easily maintained seal between such a grate system and boiler. The present invention provides a solution for these problems.